[racket] arrows in macro stepper

Hi,

A simple question: what exactly are those arrows with question mark in the macro stepper? (see picture below)
I noticed that they seem to appear only if there is an occurrence of the same identifier with a different color in between (ie. in the example below, if (display it) is not there, then the second arrow is blue, and without question mark).

I couldn't find a precise explanation in the guide.

Thanks,

-- Éric

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